Mike,
I completely understand where you're coming from... Is there more than just arson involved with this that would make the sentence so stiff? (ie. tampering w/ public utilities, etc.)
A cousin of a friend I had a few years ago was convicted of arson (Loooong story), & given 5 years probation, with a suspended 5 year sentence (meaning if he doesnt screw up during his probation, the 5 years behind bars goes away.)
15 years for destroying a house does seem a bit lengthy... I could see maybe 5ish for someone with no prior convictions. JMHO
-Randy